Positioning device and method for detecting a laser beam

ABSTRACT

The present invention relates to a positioning device and method for detecting light of fan shaped laser beam, as well as to a positioning system comprising the device and to a light emitting device emitting the fan shaped laser beam, which enable to find a spot of a laser beam easier and quicker. The positioning device comprises a detector for detecting light of a fan shaped laser beam rotating around a propagation axis with a direction of rotation and having two detector elements arranged in a known spatial relation for outputting a detection signal when irradiated; and a position determining unit to obtain a first set of detection signals from the detector elements, determine a first time relation between the detection signals of the first set, and determine a positional relation between the detector and the propagation axis based on the first time relation.

The present invention relates to a positioning device and a positioningmethod for detecting light of fan shaped laser beam, as well as to apositioning system comprising the positioning device and to a lightemitting device emitting the fan shaped laser beam.

Various kinds of surveying instruments are used for measuring distancesand angles between objects. Hereby, several conventional surveyinginstruments use a laser source to measure the distance to or theposition of an object by performing an electro-optical measurement.

When measuring the distance or position, the operator has to verify thatthe laser beam of the laser source actually impinges on the object at adesired position. However, a laser spot, e.g. impinging on a wall, isusually quite small, and in Z-mode at a far distance a user may havedifficulty finding the laser spot with the naked eye or with aconventional photodetector. Additionally, the intensity of the laserbeam decreases over the distance so that the intensity of backscatterlight from the wall further decreases.

Therefore, due to the small size of the laser spot and the distance fromthe laser source, it may be cumbersome and sometimes even impossible tofind the laser spot with the eye or by moving around a photodetector ina target area.

Furthermore, finding a small laser spot gets even more complicated underfield conditions, such as snow, rain and wind, in which a quick andsecure detection is desired.

Therefore, the need arises for a positioning device and positioningmethod enabling to find a spot of a laser beam easier and quicker.

According to an embodiment, a positioning device comprises a detectorfor detecting light of a fan shaped laser beam rotating around apropagation axis with a direction of rotation and having at least twodetector elements arranged in a known spatial relation to one anotherfor outputting a detection signal when irradiated by the fan shapedlaser beam, and a position determining unit to obtain a first set ofdetection signals from the detector elements, to determine at least onefirst time relation between the detection signals of the first set, andto determine a positional relation between the detector and thepropagation axis based on the first time relation. Accordingly, apositional relation between the detector and the propagation axis may beobtained so that the detector may be moved towards the propagation axis,i.e. towards the center axis of rotation of the light cone produced bythe rotating fan shaped laser beam. Alternatively, the propagation axisor direction of the laser emission may be moved to the detector, if theposition of the detector is desired. Using such a detector allows thatthe laser beam, i.e. its center in the case of the fan shaped laserbeam, may be automatically guided by the detector output. Further, apartfrom visible laser light, it is also possible to use infrared ornear-infrared laser light, for which several small and low cost lasersources exist. For example, according to the positional relationship, itmay be determined whether the detector is positioned to the left orright of the center of the fan shaped laser beam, i.e. the propagationaxis, or above or below of the center of the fan shaped laser beam.

According to an advantageous example, the first set of detection signalsis obtained from detector elements arranged along a first line and theposition determining unit is adapted to obtain a second set of detectionsignals from detector elements arranged along a second line. Further,the first and second lines are not parallel with respect to each anotherand the position determining unit determines at least one second timerelation between the detection signals of the second set. Accordingly,in addition to the first time relation based on detector elementsarranged along a first line, a second time relation based on detectorelements arranged along a second line may be obtained so that with eachset an area may be defined, in which the detector is placed with respectto the propagation axis, whereby the positional relationship between thedetector and the propagation axis can be more concretely specified bythe two areas. Preferably, the first line and the second line areperpendicular with respect to each other to define a quadrant in aplane, in which the detector is located.

According to another advantageous example, the first time relation is afirst time sequence of the detection signals of the first set and theposition determining unit is adapted to determine one of at least twosegments of a plane intersecting the propagation axis, in which thedetector is located. Accordingly, segments of a plane intersecting thepropagation axis may be defined. For example, it may be determinedwhether the detector is placed in a right or left semicircle segment ofthe base of the light cone produced by the rotating fan shaped laserbeam using the known direction of rotation and the knowledge of whichdetector element detects light first.

According to another advantageous example, the second time relation is asecond time sequence of the detection signals of the second set and theposition determining unit is adapted to determine one of at least foursegments of the plane intersecting the propagation axis, in which thedetector is located, based on the first time sequence and the secondtime sequence. Accordingly, in addition to the first time sequence,determining for example a left or right semicircle segment, the secondtime sequence may determine an upper or lower semicircle segment of theplane. Therefore, by determining an overlap of the two semicirclesegments obtained from the first time sequence and the second timesequence, it is possible to determine one of four segments, e.g. aquarter circle segment, of the base of the light cone produced by therotating fan shaped laser beam.

According to another advantageous example, the detector includes atleast three detector elements, a first connecting line between a firstone of the detector elements and a second one of the detector elementshaving a first predetermined length not being parallel to a secondconnecting line between a third one of the detector elements and thesecond detector element having a second predetermined length, and thefirst set of detection signals is obtained from the first and the seconddetector elements and the second set of detection signals is obtainedfrom the second and third detector elements. Accordingly, by using threedetector elements the above described advantages may be achieved, namelyit may be determined with one measurement, in which of four segments ofthe plane intersecting the propagation axis, a detector is placed.

According to another advantageous example, the position determining unitis adapted to obtain the first set of detection signals with thedetector having a first orientation and to obtain the second set ofdetection signals with the detector having a second orientation rotatedwith respect to the first orientation. Accordingly, the same advantagesas described above may be achieved with only two detector elementsmeasuring light from the rotating fan shaped laser beam twice with twomeasurements at different orientations. Similar to the above, the twoorientations are preferably perpendicular to each other.

According to another advantageous example, the position determining unitis adapted to determine a repetition time interval between two detectionsignals from the same detector element and to determine an angularfrequency of the fan shaped laser beam based thereon. Accordingly, bysimply measuring the time between two detection signals from the samedetector element, e.g. after a 180 degree rotation of the fan shapedlaser beam, the angular velocity may be derived.

According to another advantageous example, the position determining unitis adapted to determine a first time interval between the detectionsignals of the first set and the second time interval between thedetection signals of the second set, to determine, based on the angularvelocity of the fan shaped laser beam and the first and second timeintervals of a plurality of detector elements, at least two anglesbetween the detector elements, and to determine, based on the twodetector element angles and the spatial relation of the detectorelements, a distance of the detector to the propagation axis.Accordingly, by determining the two angles between the detectors of thefirst set and the detectors of the second set the distance of thedetector to the propagation axis may be determined with the knowledge ofthe spatial relation between the detector elements. Therefore, thedetector may be moved by this distance in the direction of thepropagation axis or the propagation axis may be directed on thedetector, whichever is desired, to achieve an overlap of the center ofthe light cone produced by the rotating laser beam with the detector.Consequently, it is also possible to adjust the direction of thepropagation axis automatically to the detector, since the distance tothe detector and positional relation between the detector and thepropagation axis, i.e. the segment in which the detector is placed, areknown and may be communicated from the positioning device to a laseremitter emitting the fan shaped laser beam.

According to another advantageous example, the position determining unitis adapted to obtain a third and fourth set of detection signals withthe propagation axis of the fan shaped laser beam of a laser emittertilted by an angle with respect to the orientation of the propagationaxis for obtaining the first set and second set of detection signals; todetermine a third time interval between the detection signals of thethird set and a fourth time interval between the detection signals ofthe fourth set; to determine, based on the angular velocity of the fanshaped laser beam and the third and fourth time intervals of a pluralityof detector elements, two other angles between the detector elements; todetermine, based on the two other detector element angles and thespatial relation of the detector elements, a second distance of thedetector to the tilted propagation axis; and to determine, based on thedistance and the second distance, a position of the detector withrespect to the laser emitter. Accordingly, by performing twomeasurements with two different propagation axis orientations, thedistance from the detector to the laser emitter and the distance fromthe laser emitter to the intersection of the propagation axis with theplane, in which the detector is located, may be obtained by simple meanswithout previous knowledge of the rough distance between the laseremitter and the detector.

According to another advantageous example, the position determining unitis adapted to determine a reference angle of one of the detectorelements with respect to a reference orientation and to determine aposition of the detector relative to the propagation axis of thereference orientation based on the reference angle and the distance ofthe detector to the propagation axis. Accordingly, a referencecoordinate system, e.g. a coordinate system aligned with the directionof the gravitational force, may be defined to obtain an absoluteposition of the detector.

According to another advantageous example, the detector includes atleast one level sensor for indicating at least one reference orientationof the detector in space. Accordingly, the level sensor may indicate thedirection of the gravitational force so that an absolute referenceorientation in space may be defined that may be compared to otherpositions, e.g. obtained with GPS.

According to another advantageous example, the positioning devicecomprises a laser emitter for emitting the fan shaped laser beamrotating around the propagation axis, i.e. the laser emission axis, withthe direction of rotation. Accordingly, interactions between thepositioning device determining the positional relation between itsdetector and the propagation axis of the laser light emitted by thelaser emitter and the laser emitter itself may be defined. For example,the positioning device may wirelessly communicate with the laser emitterto change its propagation axis or increase or decrease the opening angleof the light cone produced by the rotating fan shaped laser beam.

According to another embodiment, a method comprises detecting light of afan shaped laser beam rotating around a propagation axis with adirection of rotation by a detector with at least two detector elementsarranged in a known spatial relation to one another and outputting adetection signal when irradiated by the fan shaped laser beam; obtaininga first set of detection signals from the detector elements; determiningat least one first time relation between the detection signals of thefirst set; and determining a positional relation between the detectorand the propagation axis based on the first time relation. Accordingly,a positional relation between the detector and the propagation axis maybe obtained so that the detector may be moved towards the propagationaxis, i.e. the center of rotation on the rotation axis of the light coneas discussed above. Using the method allows that a laser beam may beautomatically guided by the detector output.

According to another embodiment, a positioning system, comprises a laseremitter for emitting a fan shaped laser rotating around a propagationaxis with a direction of rotation; a detector having at least twodetector elements arranged in a known spatial relation to one anotherfor outputting a detection signal when irradiated by the fan shapedlaser beam; a position determining unit to obtain a first set ofdetection signals from the detector elements, to determine at least onefirst time relation between the detection signals of the first set, andto determine a positional relation between the detector and thepropagation axis based on the first time relation. Accordingly, the sameadvantages as described above may be achieved including a co-operationbetween the laser emitter and the position determining unit.

According to another embodiment, a light emitting device comprises alaser emitter for emitting a fan shaped laser beam rotating around apropagation axis with a predetermined direction of rotation.Accordingly, a laser beam may be provided that can be easier detected bya detector, since the size of the laser spot is greatly increased,especially when the distance between the laser emitter and an object, onwhich the laser spot should be detected, is large.

According to another embodiment, a program may be provided includinginstructions adapted to cause data processing means to carry out amethod with the above features.

According to another embodiment, a computer readable medium may beprovided, in which a program is embodied, where the program is to make acomputer execute the method with the above features.

According to another embodiment, a computer program product may beprovided, comprising the computer readable medium.

Further advantageous features of the invention are disclosed in theclaims.

FIG. 1 illustrates a positioning device and a laser emitter according toembodiments of the invention.

FIGS. 2A and 2B illustrate a detector of the positioning device and itsoperation in more detail.

FIG. 3 illustrates operations of a method for determining a positionalrelation according to an embodiment of the invention.

FIG. 4 illustrates operations of a method for determining the locationof a detector according to a specific embodiment of the invention.

FIG. 5 illustrates another detector of the positioning device accordingto another embodiment of the invention.

FIG. 6 illustrates a diagram for explaining how a positional relationbetween a detector and a propagation axis may be determined.

FIG. 7 illustrates operations of a method for obtaining a distancebetween a detector and the propagation axis of a laser beam according toanother embodiment of the invention.

FIG. 8 illustrates a position of a detector with respect to the fanshaped laser beam according to a specific embodiment of the invention.

FIG. 9 illustrates a diagram explaining the embodiment shown in FIG. 8in more detail.

FIGS. 10A and 10B illustrate a change in the arrangement of thepropagation axis for obtaining a position of a detector with respect toa laser emitter according to another embodiment of the invention.

FIG. 11 illustrates elements of a position determining unit and adetector according to an embodiment of the invention.

Preferred embodiments of the invention are described with reference tothe figures. It is noted that the following description containsexamples only and should not be construed as limiting the invention.

Embodiments of the invention generally relate to obtaining a positionalrelation between a detector of a positioning device and a propagationaxis or source of a laser beam, particularly of a fan shaped laser beamrotating around the propagation axis emitted by a laser emitter. Brieflysaid, in this process a positioning device with a detector havingseveral detector elements is used to locate a rotating fan shaped laserbeam. Generally, the laser beam will impinge on the detector elementsduring its rotation generating detector signals, and the characteristicsof the detector signals, e.g. time sequence, time relation, etc., can beemployed. For example, based on a known direction of rotation and afterobtaining a time relation between detection signals from the detectorelements generated by the fan shaped laser beam impinging on them, thedetector is located with respect to the propagation axis of the fanshaped laser beam.

This detection can, for example, be either used to move the detectortowards the center of rotation of the laser beam, as to determine theposition of the detector with respect to the center of rotation of thelaser beam.

FIG. 1 illustrates elements of a positioning device 100 according to anembodiment of the invention, comprising a detector 120 and a positiondetermining unit 130.

The detector 120 detects light of a laser emitter 140. In particular,according to this embodiment, the detector 120 detects light of a fanshaped laser beam rotating around a propagation axis with a direction ofrotation.

For example, the laser emitter 140 emits the fan shaped laser beam andmeans are provided for rotating the beam around the propagation axis. Indetail, the laser emitter 140 may be part of a light emitting device, inwhich a rotatable cylindrical lens or another rotatable diffractionstructure, such as a grating or aperture, may be provided in the laserbeam for fanning the laser beam. The cylindrical lens is arrangedsuitably to rotate around the direction of propagation, i.e. around thepropagation axis of the laser. In rotation, the fan shaped laser beamproduces a cone of light with the propagation axis being the center axisof rotation.

The emitted light of the fan shaped laser beam may then be detected bythe detector 120 of the positioning device 100, which can be placed at afar distance from the laser emitter 140. The detector 120 comprises atleast two detector elements, for example detector element A and detectorelement B as shown in FIG. 1. The detector elements A and B are arrangedin a known spatial relation to one another and may each output adetection signal when irradiated by the fan shaped laser beam.

The detector elements may be realized by any known photodetector, suchas a photodiode, avalanche photodiode or charge coupled device (CCD)element(s).

Once light of the fan shaped laser beam is detected at one or moredetector elements, one or more detection signals may be output by thedetector 120 to the position determining unit (PDU) 130, as can be seenfor example in FIG. 1.

The position determining unit 130 is acting as a controller andprocessor and may be realized by a hardware arrangement, such as byhardwired circuits, or ASICs (application specific integrated circuits)or software or any suitable combination of the above. An implementationexample is given later with respect to FIG. 11. The functions performedby the position determining unit 130 will be described in the following.

As can be seen in FIG. 1, the position determining unit 130 may obtain afirst set of detection signals from the detector 120 detected by thedetector elements, for example, through an I/O interface.

The position determining unit 130 determines at least one first timerelation between the detection signals of the first set of detectionsignals from the detector elements and may then determine a positionalrelation between the detector and the propagation axis based on thefirst time relation and the direction of rotation. The first timerelation may implicitly already comprise the direction of rotation,since the time relation can indicate a time difference as well as timesequence, as will be described below.

For example, as can be seen in FIG. 1, when the fan shaped laser beamrotates in a clockwise direction, as indicated in FIG. 1, light willfirst irradiate detector element A and then detector element B. Based onthis information, the position determining unit can determine that thedetector 120 is placed to the right with respect to the propagationaxis, i.e. the center of the circle in FIG. 1.

Therefore, a positional relation between the detector and thepropagation axis is obtained so that, if the detector is placed on anobject to be measured, the propagation axis may be moved in thedirection of the detector. Or vice versa, if the laser beam should notbe moved, the detector may be moved in the direction of the center ofthe cone produced by the fan shaped laser beam. For clarification of theperspective shown in FIG. 1, it is noted that the circle shown in FIG. 1is the base part of a light cone produced by the rotating fan shapedlaser beam.

In FIG. 1, the positioning device 100 is shown as two separate elements,namely the detector 120 and the position determining unit 130. However,it will be appreciated by those skilled in the art that the detector 120and the position determining unit 130 may also be integrated in oneelement to form the positioning device 100.

Further, it is noted that the positioning device 100 may also comprisethe laser emitter 140 which then may be regarded as a positioning systemwith the elements 120, 130 and 140 shown in FIG. 1 and described indetail above.

Still further, the laser emitter 140 may be part of a surveyinginstrument, such as a theodolite, video tacheometer, or total station orany other kind of optical instrument for determining a position of anobject.

In another embodiment, the detector can be used as a 2D-layout device.For example, the detector detects certain positions, such as edge pointsor other characteristic features, which may be used to define astructure to be build. To be more specific, the outline of a building inthe field may be defined by positions measured by the detector.Therefore, the outline of a building may be defined or planned on afield before the actual building is built.

A more detailed explanation of the functions performed by thepositioning device 100 including the detector 120 and the positiondetermining unit 130 will be described below with respect to FIGS. 2Aand 2B.

FIGS. 2A and 2B illustrate the light cone of the rotating fan shapedlaser beam on a plane, in which a detector is placed.

In detail, the fan shaped laser beam 210 in FIGS. 2A and 2B is shown asa grey bar rotating in a coordinate system, in which the detector 220with the detector elements A and B is placed. In rotation, the fanshaped laser beam 210 with its propagation axis perpendicular to theplane and intersecting the origin of the coordinate system, covers thecircle indicated by reference numeral 230, which represents the base ofthe light cone produced by the fan shaped laser beam 210 with the centeraxis of rotation being the propagation axis.

As indicated above, it may be seen from FIG. 2A that when the fan shapedlaser beam 210 rotates in the clockwise direction as indicated by thearrow 250, a detection signal may first be obtained from detectorelement A and then after a further rotation angle another detectionsignal may be output from detector element B. Therefore, a first set ofdetection signals may be obtained from detector elements A and Barranged along a first line. Thereby, it may be determined from thesequence of obtained detection signals, namely detection signal fromdetector element A received first and detection signal from detectorelement B received second, that the detector is placed in a semicircleto the right of the propagation axis which is indicated by hatching inFIG. 2A.

In addition to the first set of detection signals, the positiondetermining unit 130 may obtain a second set of detection signals fromdetector elements arranged along a second line, wherein the first andsecond lines are not parallel with respect to one another. An example ofa second set of detection signals will be described with respect to FIG.2B.

In FIG. 2B the same fan shaped laser beam 210 with the same direction ofrotation is shown covering the circle 230 in rotation. However, incontrast to FIG. 2A, the detector 220 is rotated by 90 degrees so thatthe detector elements A′ and B′ are again arranged along a line, but nowalong a second line in horizontal direction and not anymore verticaldirection as before.

As can be seen from FIG. 2B, when the fan shaped laser beam rotates inthe clockwise direction, the detector element B′ is irradiated first bythe laser light and outputs a detection signal and then the detectorelement A′ is irradiated. Receiving these signals as a second set ofdetection signals, the position determining unit 130 may determine asecond time relation between the detection signals of the second set,which indicates in this example that the detector 120 is placed in anupper semicircle with respect to the propagation axis, namely the originof the coordinate system. Here again, the hatched semicircle indicatesthe semicircle determined as the area, in which the detector is placedwith respect to the propagation axis.

Therefore, by combining the two measurements in FIGS. 2A and 2B, aquarter circle may be defined in which the detector 220 is located,namely the quarter circle in the upper right quadrant of the coordinatesystem. Consequently, the detector may be moved in the direction of thecenter of the coordinate system, which is where the laser beamintersects with the plane, if the laser beam would not be fanned.Furthermore, as described above, also the laser beam or the fan shapedlaser beam may be moved in the direction of the detector so thatautomatic tracking of the detector may be realized by measuring thelocation of the detector, moving the laser beam in the direction of thedetector and measuring the location of the detector again in a recursivemanner.

In other words, as described with respect to FIG. 2A, the first timerelation is a first time sequence of detection signals of the first setof detection signals and the position determining unit 130 determinesone of at least two segments of a plane intersecting the propagationaxis, in which the detector is located, e.g. the hatched semicircle inFIG. 2A.

Further, if additionally a second set of detection signals is obtainedas described with respect to FIG. 2B, the second time relation is asecond time sequence of the detection signals of the second set and theposition determining unit determines one of at least four segments ofthe plane intersecting the propagation axis, in which the detector islocated, based on the first time sequence and the second time sequence.The one of the four segments in the example of FIGS. 2A and 2B is thequarter circle hatched in both figures located in the upper rightquadrant of the coordinate system.

It is noted that the detector 120 does not necessarily have to berotated by 90 degrees but also other rotation angles of the detectorelements may be used to get satisfying results.

In the following, operations of the positioning device will be describedwith regard to FIG. 3. FIG. 3 illustrates a flow diagram of operationsof a method for obtaining a positional relation between a detector and apropagation axis of a laser beam, such as during operation of thepositioning device 100 in FIG. 1.

In a first operation 310, when starting operations, a detector, e.g. thedetector 120 of FIG. 1 or the detector described with respect to FIG. 5later, detects light of a fan shaped laser beam rotating around apropagation axis with direction of rotation. As described above, thedetector has at least two detector elements arranged in a known spatialrelation to one another and outputs a detection signal when irradiatedby the fan shaped laser beam, which may be emitted from a laser emitter,e.g. the laser emitter 140 shown in FIG. 1. Preferably, the direction ofrotation of a fan shaped laser beam is known. For example, a positioningsystem may always use a clockwise rotation or alternatively thedirection of rotation may be communicated to the positioning device fromthe laser emitter by either fixed line or a wireless connection, whichwill be described in more detail later with respect to FIG. 11.

In a subsequent operation 320, a first set of detection signals from thedetector elements is obtained. In a simple case, the set comprises twodetection signals, for example one detection signal from detectorelement A and another detection signal from detector element B of thedetector 120 of FIG. 1. Then, the detection signals may be sent to theposition determining unit 130 for further processing.

Processing may include, in an operation 330, determining at least onefirst time relation between the detection signals of the first set. Forexample, a time relation may be a time sequence indicating which signalhas been received first and the time difference between the signals.

In an operation 340, a positional relation between the detector and thepropagation axis is determined based on the first time relation and thedirection of rotation. For example, as explained above, knowing thedirection of rotation and the sequence of the detection signals comingfrom the detector elements, it may be determined where on a plane adetector is located with respect to the propagation axis. For example,as shown in FIG. 2A, the position determining unit 130 may determinethat the detector is located in a semicircle positioned to the right ofthe propagation axis of the fan shaped laser beam.

Optionally, to further narrow down the area, in which the detector isplaced, a second measurement may be performed to obtain a second set ofdetection signals, which has been described in detail with respect toFIG. 2B, in which the first set of detection signals has been obtainedin a first orientation and the second set of detection signals has beenobtained in a second orientation rotated with respect to the firstorientation.

FIG. 4 illustrates a flow diagram summarizing the examples describedwith respect to FIGS. 2A and 2B.

In the flow diagram of FIG. 4, t denotes the time when light of the fanshaped laser beam is detected. More specifically, t_(A) denotes the timewhen light is received by the detector element A and t_(B) denotes thetime when light has been received by the detector element B. Similarly,t_(A′) and t_(B′) are the times when light is received by detectorelements A′ and B′, which may be the same detector elements as A and Bbut of a second measurement after the detector has been rotated, or maybe other detector elements. It is noted that an absolute measurement oftime is not necessary and the relative time between the detectorelements should be sufficient to achieve the advantages of theinvention.

In operation 410, it is determined whether light has been received firstby detector element A, which means t_(A)<t_(B).

If this is true, the flow proceeds to operation 415, in which it isdetermined that the detector is placed in a right semicircle withrespect to the propagation axis, as can be seen in FIG. 2A.Subsequently, the flow proceeds to operation 420, in which the detectoris rotated, as illustrated in FIG. 2B by, for example, 90 degrees sothat the first line and the second line are perpendicular.

In the next operation 425, it is determined whether t_(A′) is longerthan the time t_(B′). If this determination is positive, the flowproceeds to operation 435 or otherwise if negative to operation 430.

In operation 430, it is then determined that the detector is placed in alower semicircle with respect to the propagation axis. On the otherhand, in operation 435, it is determined that the detector is placed inan upper semicircle as previously discussed with respect to FIG. 2B.

With the knowledge that the detector is placed in a right semicircle andis placed in an upper semicircle with respect to the propagation axis,it follows that the detector is located in a quarter circle, namely inan upper right quadrant of the coordinate system shown in FIGS. 2A and2B.

Considering the case in which the time t_(B) is shorter than the timet_(A), the determination in operation 410 is negative and the flowproceeds to operation 440. In operation 440, it is determined that thedetector is in a left semicircle with respect to the propagation axis,namely the non-hatched semicircle in FIG. 2A. That means, the casedescribed in the right arm of FIG. 4 is not shown in FIGS. 2A and 2B.

In the following operation 445, the detector is rotated, preferably by90 degrees. In operation 450 it is determined whether time t_(A′) islonger than time t_(B′). If this is true, the flow proceeds to operation460, in which it is determined that the detector is in the uppersemicircle. If this is not true the flow proceeds to operation 455, inwhich it is determined that the detector is in the lower semicircle.

Therefore, using the simple flow shown in FIG. 4, a rough position ofthe detector with respect to the propagation axis may be determined sothat either the detector or the laser beam may be moved with respect toeach other, if desired.

In the following, FIG. 5 illustrates another embodiment of theinvention, in which the detector comprises three detector elements.

In FIG. 5, the fan shaped laser beam is denoted with reference numeral510 and the detector with reference numeral 520. The detector 520comprises three detector elements, namely detector element A, detectorelement B and detector element C. Similar to the above, a detectorelement may be by any known photodetector, such as a photodiode,avalanche photodiode or charge coupled device (CCD) element(s).

In the herein described example, the detector 520 comprises threedetector elements, a first connecting line between a first detectorelement A and a second detector element C having a first predeterminedlength a, and a second connecting line between a third detector elementB and the second detector element C having a second predetermined lengthb, wherein the first and the second connecting lines are not parallel.Here, the first set of detection signals is obtained from the first andthe second detector elements A and C and the second set of detectionsignals is obtained from the second and the third detector elements Cand B.

It is noted that the three detector elements are preferably oriented asshown in FIG. 5, i.e. detector elements A and C in a first vertical lineand detector elements C and B in a second horizontal line perpendicularto the vertical line.

Therefore, the position determining unit may obtain the first set ofdetection signals with the detector having a first orientation and thesecond set of detection signals with the detector having a secondorientation without a rotation necessary. However, it is noted that thiscase leads to the same information as using only two detector elementsbut two measurements, wherein the two detector elements are rotated froma first orientation to a second orientation. Further, those skilled inthe art will appreciate that various orientations exist to achieve theadvantageous of the invention and that the detector is not limited totwo or three detector elements.

Similar to the above, it may also be seen from FIG. 5 that when adetection signal is first detected by detector element A, then adetection signal is detected by detector element C and finally adetection signal is detected by detector element B, it may be determinedthat the detector is placed in a quarter circle in the upper rightquadrant of the coordinate system shown in FIG. 5.

Until now, examples have been described, in which the rough location ofa detector in a coordinate system is determined. However, thepositioning device and positioning method described herein may furtherbe adapted to determine the exact position of a detector, which will bedescribed in the following with respect to FIG. 6.

To derive the exact position, the angular velocity ω of the rotating fanshaped laser beam may be used. The angular velocity may be obtaineddirectly from the laser emitter, or more specifically from the rotationspeed of the cylindrical lens placed in front of the laser emitter,which has been described above.

Furthermore, the angular velocity of the fan shaped laser beam may alsobe determined by the position determining unit itself by determining arepetition time interval between two detection signals from the samedetector element.

For example, consider detector element A and a clockwise rotation of thefan shaped laser beam, it can be seen from FIG. 5 or also from FIGS. 1,2A, and 2B, that when the angular velocity is constant, a timedifference between two detection signals from detector element Acorresponds to a rotation of the fan shaped laser beam by 180 degrees.Therefore, the angular velocity may easily be derived by the detectorwithout any knowledge of the rotating cylindrical lens.

In short, the position of the detector in the coordinate system shown inFIG. 5 with the center of rotation of the light cone of the fan shapedlaser beam being the origin, may be derived as follows.

First, the position determining unit determines a first time intervalbetween the detection signals of the first set and a second timeinterval between the detection signals of the second set. In the exampleof FIG. 6, the first time interval is obtained from the detectionsignals from detector element A and detector element C and the secondtime interval is obtained from the detection signals from the detectorelement C and the detector element B.

Then, the position determining unit may determine two angles, based onthe angular velocity of the fan shaped laser beam and the first andsecond time intervals obtained from the corresponding detector elements.These two angles correspond to the angles α and β in FIG. 6, which mayeasily be derived when knowing the time needed for example for a 180 or360 degree rotation, i.e. the angular velocity, and the time the fanshaped laser beam needs from detector element A to B and the time fromdetector element C to B.

As will be show in detail mathematically in the following, based on thetwo angles and the spatial relation of the detector elements, namelytheir lengths a and b, a distance of the detector to the propagationaxis may be derived.

FIG. 6 illustrates a diagram with an x-y-coordinate system, in which theorigin of the coordinate system is the center of rotation, namely theintersection of a plane, in which a detector is located, with thepropagation axis. The detector in FIG. 6 is exemplified by the detectorelements A, B and C, wherein the line between A and C has a length a andthe line between detector elements C and B has a length b.

In the following mathematical derivation of the position of the detectorit is assumed for simplification that the length a equals the length band that the first connecting line between a and c is parallel to they-axis and the second connecting line between C and B is parallel to thex-axis. Further, the angular velocity ω is assumed to be constant.

Below it is shown how x₀ being the distance in x-direction betweendetector element C and the origin and y₀ being the distance in thex-direction between the detector element C and the origin are obtainedfrom the angles α and β and the length between the detector elements a.

The calculation is as follows:

$\begin{matrix}{{{\tan \; \alpha} = \frac{a^{\prime}}{r}}{{\tan \; \beta} = {{\frac{b^{\prime}}{r}->\frac{a^{\prime}}{b^{\prime}}} = \frac{\tan \; \alpha}{\tan \; \beta}}}} & (1)\end{matrix}$

With the law of sine and sum formula:

$\begin{matrix}{{\frac{a^{\prime}}{a} = {\frac{\sin \left( {{90{^\circ}} - \alpha - \gamma} \right)}{\sin \left( {{90{^\circ}} + \alpha} \right)} = {\frac{\sin \left( {{90{^\circ}} - \delta} \right)}{\sin \left( {{90{^\circ}} + \alpha} \right)}\mspace{14mu} \left( {\delta = {\alpha + \gamma}} \right)}}}{\frac{\alpha^{\prime}}{a} = {\frac{{\sin \; 90{{^\circ}cos}\; \delta} - {\sin \; {\delta cos90{^\circ}}}}{{\sin \; 90{{^\circ}cos}\; \alpha} + {\sin \; {\alpha cos90{^\circ}}}} = {\frac{\cos \; \delta}{\cos \; \alpha} = \frac{\cos \left( {\alpha + \gamma} \right)}{\cos \; \alpha}}}}\begin{matrix}{\frac{a^{\prime}}{a} = \frac{{\cos \; {\alpha cos\gamma}} - {\sin \; {\alpha sin}\; \gamma}}{\cos \; \alpha}} \\{= {{\cos \; \gamma} - {\frac{\sin \; \alpha}{\cos \; \alpha}\sin \; \gamma}}} \\{= {{\cos \; \gamma} - {\tan \; {\alpha sin}\; \gamma}}}\end{matrix}} & (2) \\{{a^{\prime} = {a\left( {{\cos \; \gamma} - {\tan \; \alpha \; \sin \; \gamma}} \right)}}{\frac{b^{\prime}}{a} = \frac{\sin \left( {\gamma - \beta} \right)}{\sin \left( {{90{^\circ}} + \beta} \right)}}\begin{matrix}{\frac{b^{\prime}}{a} = \frac{{\sin \; {\gamma cos}\; \beta} - {\sin \; \beta \; \cos \; \gamma}}{{\sin \; 90{{^\circ}cos}\; \beta} + {\sin \; \beta \; \cos \; 90{^\circ}}}} \\{= {{\sin \; \gamma} - {\frac{\sin \; \beta}{\cos \; \beta}\cos \; \gamma}}} \\{= {{\sin \; \gamma} - {\tan \; {\beta cos\gamma}}}}\end{matrix}{b^{\prime} = {a\left( {{\sin \; \gamma} - {\tan \; {\beta cos}\; \gamma}} \right)}}} & (3)\end{matrix}$

(2): (3)=(1), that means substituting equations (2) and (3) intoequation (1) leads to

$\begin{matrix}{{\frac{a^{\prime}}{b^{\prime}} = {\frac{a\left( {{\cos \; \gamma} - {\tan \; \alpha \; \sin \; \gamma}} \right)}{a\left( {{\sin \; \gamma} - {\tan \; {\beta cos}\; \gamma}} \right)} = \frac{\tan \; \alpha}{\tan \; \beta}}}{{{\tan \; {\alpha sin}\; \gamma} - {\tan \; \alpha \; \tan \; \beta \; \cos \; \gamma}} = {{\tan \; \beta \; \cos \; \gamma} - {\tan \; {\beta tan}\; {\alpha sin\gamma}}}}{{\sin \; {\gamma \left( {{\tan \; \alpha} + {\tan \; {\alpha tan}\; \beta}} \right)}} = {\cos \; {\gamma \left( {{\tan \; \beta} + {\tan \; {\alpha tan\beta}}} \right)}}}{\frac{\sin \; \gamma}{\cos \; \gamma} = {{\tan \; \gamma} = \frac{{\tan \; \beta} + {\tan \; {\alpha tan\beta}}}{{\tan \; \alpha} + {\tan \; {\alpha tan\beta}}}}}} & (4) \\{{{{{\tan \; \gamma} = \frac{\left( {\frac{1}{\tan \; \alpha} + 1} \right)}{\left( {\frac{1}{\tan \; \beta} + 1} \right)}};{\gamma = {\arctan \frac{\left( {\frac{1}{\tan \; \alpha} + 1} \right)}{\left( {\frac{1}{\tan \; \beta} + 1} \right)}}}}{\tan \; \gamma} = \frac{y_{0}}{x_{0}}}{y_{0} = {x_{0}\tan \; \gamma}}} & (5) \\{{\tan \left( {\alpha + \gamma} \right)} = \frac{y_{0} + a}{x_{0}}} & (6)\end{matrix}$

(5) in (6)

$\begin{matrix}{{{\tan \left( {\alpha + \gamma} \right)} = \frac{{x_{0}\tan \; \gamma} + a}{x_{0}}}{x_{0} = \frac{a}{{\tan \left( {\alpha + \gamma} \right)} - {\tan \; \gamma}}}} & (7)\end{matrix}$

(4) in (7)

$\begin{matrix}{x_{0} = \frac{a}{{\tan\left( {\alpha + {\arctan\left( \frac{\frac{1}{\tan \; \alpha} + 1}{\frac{1}{\tan \; \beta} + 1} \right)}} \right)} - \frac{\frac{1}{\tan \; \alpha} + 1}{\frac{1}{\tan \; \beta} + 1}}} & (8) \\{y_{0} = {x_{0}\frac{\frac{1}{\tan \; \alpha} + 1}{\frac{1}{\tan \; \beta} + 1}}} & (9)\end{matrix}$

As can be seen from equations (8) and (9), these equations onlydependent on the angles α and β and the length a, which is given by thedetector geometry.

As described above, the angles α and β may be easily calculated byknowing the angular velocity of the fan shaped laser beam and the timedifference between light detected by detector element A and lightdetected by detector element C and the time difference between lightdetected by detector element C and light detected by detector element B,respectively.

In the following, an example is given to check the equations (8) and(9). Here it is assumed that x₀=1000 mm, y₀=250 mm and a=30 mm, and αand β are wanted.

ɛ = γ − β $\begin{matrix}{{\tan \; ɛ} = {\frac{y_{0}}{x_{0} + a}->ɛ}} \\{= {\arctan \left( \frac{y_{0}}{x_{0} + a} \right)}} \\{= {\arctan \left( \frac{250\mspace{14mu} {mm}}{{1000\mspace{14mu} {mm}} + {30\mspace{14mu} {mm}}} \right)}} \\{= {13,6429148{^\circ}}}\end{matrix}$${\tan \; \gamma} = {{\frac{y_{0}}{x_{0}}->\gamma} = {{\arctan \left( \frac{y_{0}}{x_{0}} \right)} = {{\arctan \left( \frac{250\mspace{14mu} {mm}}{1000\mspace{14mu} {mm}} \right)} = {14,03624347{^\circ}}}}}$β = γ − ɛ = 14, 03624347^(∘) − 13, 6429148^(∘) = 0, 393328667^(∘)$\begin{matrix}{{\tan \left( {\alpha + \gamma} \right)} = {\frac{y_{0} + a}{x_{0}}->{\alpha + \gamma}}} \\{= {\arctan \left( \frac{y_{0} + a}{x_{0}} \right)}} \\{= {\arctan \left( \frac{{250\mspace{14mu} {mm}} + {30\mspace{14mu} {mm}}}{1000\mspace{14mu} {mm}} \right)}} \\{= {15,64224646{^\circ}}}\end{matrix}$ $\begin{matrix}{\alpha = {{15,64224646{^\circ}} - \gamma}} \\{= {{15,64334646{^\circ}} - {14,03624347{^\circ}}}} \\{= {1,60600299{^\circ}}}\end{matrix}$

The obtained results for the angles α and β may then be plugged inequations (8) and (9) to check their validity.

For x₀ it may found

$x_{0} = \frac{a}{{\tan\left( {\alpha + {\arctan\left( \frac{\frac{1}{\tan \; \alpha} + 1}{\frac{1}{\tan \; \beta} + 1} \right)}} \right)} - \frac{\frac{1}{\tan \; \alpha} + 1}{\frac{1}{\tan \; \beta} + 1}}$$\frac{30\mspace{14mu} {mm}}{\begin{matrix}{{\tan \left( {{1,60600299{^\circ}} + {\arctan \left( \frac{\frac{1}{\tan \; 1,60600299{^\circ}} + 1}{\frac{1}{\tan \; 0,393328667{^\circ}} + 1} \right)}} \right)} -} \\{\frac{\frac{1}{\tan \; 1,60600299{^\circ}} + 1}{\frac{1}{\tan \; 0,393328667{^\circ}} + 1} = {1000\mspace{14mu} {mm}}}\end{matrix}}$

As described above, it has been assumed that the first connecting lineand the second connection line are parallel to the x-axis and y-axis,respectively.

Therefore, a relative position, namely a position in a coordinate systemdefined by the connecting lines of the detector elements is achieved.

Further, it may be desired to obtain the position in another referencecoordinate system, for example a reference coordinate system using thegravitational force as one axis.

In one embodiment, the position determining unit determines a referenceangle of one of the detector elements with respect to a referenceorientation, and determines a position of the detector relative to thepropagation axis and the reference orientation based on the referenceangle and the distance of the detector to the propagation axis.

For example, as described above the reference orientation may have thesame direction as the gravitational force or may be perpendicular to thegravitational force so that a reference coordinate system may be usedthat is comparable to other known reference coordinate systems, such asthe one used in a global positioning system (GPS). A level sensor may beused for indicating at least one reference orientation of the detectorin space, for example. The level sensor may be provided in the detectoras will be later described in FIG. 11.

In the flowchart described below with respect to FIG. 7, the operationsof the above described calculation are summarized by referring to theposition determining unit 130 and the detector shown in FIG. 6.

It will be appreciated by those skilled in the art that equivalentresults to the results obtained with the detector shown in FIG. 6 withthree detector elements may also be obtained with the detectors 120, 220shown in FIGS. 1, 2A and 2B by rotating this detector 120, 220 as shownin FIG. 2B.

The first operation in the embodiment described with respect to FIG. 7is operation 310, previously described with respect to FIG. 3. In thisoperation light of a fan shaped laser beam rotating around thepropagation axis is detected with at least two detector elementsarranged in a known spatial relation to one another. As discussed in thefollowing, it is equivalent whether two measurements with two detectorelements are taken at a different angle with respect to another orwhether a detector with three elements is used.

In an operation 720, a first set of detection signals from detectorelements arranged along a first line and a second set of detectionsignals from detector elements arranged along a second line areobtained. Preferably, the first and second lines are perpendicular withrespect to each other, which is for example the case for detector 520 ofFIG. 5 or the detector shown in FIG. 6.

In a subsequent operation 730, a repetition time interval between twodetection signals from the same detector element is determined to obtainthe angular velocity of the fan shaped laser beam. Details of thisoperation have been described above, and it is referred to the aboveexplanation to avoid unnecessary repetition.

In operation 740, a first time interval between the detection signals ofthe first set and a second time interval between the detection signalsof the second set are determined. For example, the first time intervalmay be the time interval between the detection signal from detectorelement A when light hits this detector element and the detection signalfrom detector element C when light hits the detector element C. Thesecond time interval may be correspondingly obtained from the detectionsignals from detector elements C and B when light of the fan shapedlaser beam hits these elements.

In operation 750, two angles, e.g. α and β of FIG. 6, may be determinedbased on the above angular velocity and the first and second timeintervals.

As shown in detail above, in a calculation of the position of thedetector, the two angles and the spatial relation of the detectorelements may be used in operation 760 to determine a distance of thedetector to the propagation axis, i.e. a relative position to thepropagation axis in a coordinate system having the propagation axis asorigin.

FIG. 8 illustrates a specific embodiment to easily derive the distancebetween the center of rotation, i.e. the propagation axis, and thedetector.

In FIG. 8, the fan shaped laser beam is denoted with reference numeral810 and the detector comprising the detector elements A, C and B isdenoted with reference numeral 820.

As will be seen with respect to FIG. 9, it is important in thisembodiment that the connecting line between detector elements A and C isperpendicular to the fan shaped laser beam as shown in FIG. 8. Such anorientation may be easy to achieve with a detector having three detectorelements with their connecting lines being perpendicular with respect toeach other as shown in FIG. 8. For example, from the geometry ofdetector 820, it can be derived that if two detection signals fromdetector elements C and B are outputted concurrently, both detectors areplaced on the fan shaped laser beam at the same time and the firstconnecting line between detector elements A and C is perpendicular withrespect to the fan shaped laser beam.

In other words, the time difference from detector signals from thedetector elements C and B is zero and the time difference betweendetection signals from detector elements A and C corresponds to theangle α shown in FIG. 9.

In more detail, FIG. 9 shows the geometrical relationship between thedetector elements and the coordinate system, and the distance r betweendetector element C and the origin of the coordinate system, which may bethe center of rotation of the light cone, wherein the axis of rotationis the previously described propagation axis, perpendicular to theplane.

Using the geometrical relationships shown in FIG. 9, a distance r mayeasily be obtained by

${{\tan \; \alpha} = {{\frac{a}{r}\mspace{14mu} {which}\mspace{14mu} {leads}\mspace{14mu} {to}\mspace{14mu} r} = \frac{a}{\tan \; \alpha}}},$

wherein the length a is known and a may be calculated with the knowledgeof the angular velocity using the time difference between the time ofthe detection signals from detector elements A and C.

As can be seen above, in the calculation with respect to FIGS. 8 and 9knowledge about the direction of rotation is not necessary to calculatethe distance r.

In the described embodiments, the time may be measured in the positiondetermining unit according to the generation and arrival of thedetection signals or may even be already determined in a detectorelement itself by providing the signal from the detector element to theposition determining unit with a time stamp, to name a few of possiblemethods for time measurement.

Further, x₀=r cos β and y₀=r sin β, as can be seen in FIG. 9, may beobtained with angle β, which may be measured by a grade sensor.

Before, measurements of the distance from the detector to the laserpropagation axis have been described. In the following embodiment, aposition of the detector with respect to the laser source, e.g. thelaser emitter of FIG. 1, is described with respect to FIGS. 10A and 10B.

In FIG. 10A a laser emitter 1040, which may be any suitable laser usedfor surveying instruments, and a detector 1000 at a position X1, Y1 areshown. It is noted that according to the invention, since detectors fordetecting the laser beam are used and not the naked eye, the laseremitter is not limited to visible light but also infrared light may beused which is not seen with the eye but may be detected by a detector.

In contrast to the previous FIGS. 2A, 2B, FIG. 5, FIG. 6, FIG. 8 andFIG. 9 all showing an x-y-plane of a coordinate system, in FIGS. 10A and10B a y-z-plane is shown.

At first, the positioning device determines the coordinates X1 and Y1 tothe intersection between the center of rotation and the plane, in whichthe detector is placed. This may be done as described above by obtaininga first and second set of detection signals and determining a first anda second time interval between the detection signals to obtain twoangles between the detector elements.

Next, as can be seen in FIG. 10B, the propagation axis of the laseremitter 1040 is tilted by a known angle. Here, the whole laser emittermay be tilted or simply a mirror or prism may be used to tilt thepropagation axis.

Then, the position X2, Y2 with respect to the new orientation of thetilted propagation axis, namely the position with respect to the neworigin O′, may be derived as follows.

A third and fourth set of detection signals with the propagation axis ofthe fan shaped laser beam of the laser emitter 1040 tilted by an anglewith respect to the orientation of the propagation axis when obtainingthe first set and second set of detection signals are obtained.

Subsequently, a third time interval between the detection signals of thethird set and a fourth time interval between the detection signals ofthe fourth set may be determined to derive two other angles between thedetector elements using the angular velocity of the fan shaped laserbeam so that a second distance from the detector to the tiltedpropagation axis, namely Y2, may be obtained.

It is noted that the calculation of Y2 is equivalent to the calculationof Y1, which has been described in detail with respect to FIG. 6,wherein in the present embodiment the x-coordinate does not have to beused.

As can be seen from the simple geometrical relationships in FIGS. 10Aand 10B, the distance d may be calculated by d=Y2′−Y1, whereinY2′=Y2/cos(α). When the angle α is small, which is usually the case fora large distance a₁, the difference between Y2′ and Y2 may benegligible.

Knowing the angle of tilt, α in FIG. 10B, the distance a₁ may beobtained by a₁=d/tan(α), wherein the distance b between detector andlaser emitter may be obtained using Pythagoras' theorem leading to

b=√{square root over ((a ₁ ² +Y1²))}

Therefore, the distance b between detector and laser emitter is obtainedby determining two positions of the detector 1000 with respect to twodifferent orientations of the propagation axis.

In the following, FIG. 11 is described. FIG. 11 illustrates elements ofa position determining unit and a detector according to an embodiment ofthe invention.

In detail, the position determining unit 1100 of FIG. 11 comprises acontroller 1110, a memory 1130, and an I/O interface 1150. Optionally,the position determining unit 1100 may also comprise a remotetransceiver 1140 which will be discussed in more detail later.

The detector 1120 comprises at least two detector elements A and C.Optionally, there may be more detector elements provided, such asdetector element B. Further, in one embodiment, the detector 1120 mayalso comprise a grade sensor 1125 to indicate a reference orientation,for example the direction of the gravitational field of the earth.

As described above, the positioning device may comprise the positiondetermining unit 1100 and the detector 1120 as two separate units or theposition determining unit 1100 and the detector 1120 may be integratedin one unit or only single elements of the detector may be integrated inthe position determining unit.

The controller 1110 may be realised by any kind of processing means, amicroprocessor, computer, field programmable gate array (FPGA) orintegrated circuit, such as an application specific integrated circuit(ASIC) but are not limited thereto. For example, the controller 1110 mayhave a processor running several software elements, for example,software elements corresponding to the functions described in theoperations of the methods above.

The memory 1130 may be any suitable or desirable storage device and maybe one or a combination of several of the following components, a RAM, aROM, a hard disk, an (E)EPROM, a disc, a flash memory, etc. A flashmemory may be suitable to export or import program code. The programcode stored in the memory 1130 may be a program including instructionsadapted to cause the data processing means of the controller 1110 tocarry out operations of the method described above.

The I/O interface 1150 may be adapted to receive detection signals fromthe detector 1120. Further, it is also feasible that the positiondetermining unit 1100 and the detector 1120 communicate otherinformation, such as starting the detection, stopping the detection andproviding grade sensor information to the position determining unit1100.

Therefore, as described above, the controller 1110 may receive detectionsignals from the detector 1120 through the I/O interface 1150 and maycarry out the operations of the above-described methods by referring tothe memory 1130 including the corresponding instructions.

Furthermore, a remote transceiver 1140 may be included in the positiondetermining unit 1100 to communicate with an instrument comprising thelaser emitter, such as a light emitting device or a surveyinginstrument. For example, another transceiver of a surveying instrumentfor communication with the transceiver 1140 of the position determiningunit 1100 in the positioning device may be provide with instructions forthe surveying instrument to change the laser beam position so that thelaser beam of the surveying instrument may be automatically steeredtowards the detector 1120. The communication between the surveyinginstrument and the positioning device may be realised physically byfixed lines or by a wireless connection, such as radio, WLAN, e.g. IEEE802.11 or Bluetooth or any other suitable wireless connection.

It will be appreciated by those skilled in the art that the controller,e.g. including any type of processor, can take the form of variouscombinations of processors and operating systems or a stand alonedevice. Further, the methods may be implemented on a data processingcomputer, such as a personal computer, workstation computer, main framecomputer or other computer running an operating system such as MicrosoftWindows and Windows 2000, available from Microsoft Corporation ofRedmond, Wash./USA or Solaris available from Sun Microsystems, Inc. ofSanta Clara, Calif./USA or various versions of the Unix operatingsystems such as Linux available from a number of vendors.

According to another embodiment, a program may be provided includinginstructions adapted to cause a data processor that may be part of thecontroller 1110 to carry out combinations of the above-describedoperations.

The program or elements thereof may be stored in a memory, such as a ROMor RAM or other suitable storage device, for example the memory 1130 ofFIG. 11, and retrieved by the data processor for execution.

Moreover, a computer readable medium may be provided in which theprogram is embodied. The computer readable medium may be tangible, suchas a disc or other data carrier are maybe constituted by signalssuitable for electronic, optic or any other type of transmission. Acomputer program product may comprise the computer readable medium.

The above embodiments and examples of the invention may allow performingdetection of a laser beam and obtaining a positional relation betweenthe laser beam and detector for different purposes. For example, asexplained above, the invention may be applied to surveying, wherein asurveying instrument is provided with a laser emitter and the light ofwhich is detected and analyzed by the positioning device thus realizingan automated surveying system. Therefore, fast and easy detection andautomation of this process may be achieved.

It should be understood that operations described herein are notinherently related to any particular device or unit and may beimplemented by any suitable combination of components. The devices,system and units described in detail above constitute preferredembodiments to perform the operations of the described methods. However,this may not be limited to the same.

It will be apparent to those skilled in the art that variousmodifications and variations can be made in the devices, system, unitsand methods of the invention as well as in the construction of thisinvention without departing from the scope of or spirit of theinvention.

The invention has been described in relation to particular embodimentsand examples which are intended in all aspects to be illustrative ratherthan restrictive. Those skilled in the art will appreciate that manydifferent combinations of hardware, software and firmware will besuitable for practicing the present invention.

Moreover, other implementations of the invention will be apparent tothose skilled in the art from consideration of the specification andpractice of the invention disclosed herein. It is intended that thespecification and the examples be considered as exemplary only. To thisend, it is to be understood that inventive aspects lie in less than allfeatures of a single foregoing disclosed implementation orconfiguration. Thus, the true scope and spirit of the invention isindicated by the following claims.

1. A positioning device, comprising: a detector for detecting light of afan shaped laser beam rotating around a propagation axis with adirection of rotation and having at least two detector elements (A, B)arranged in a known spatial relation to one another for outputting adetection signal when irradiated by the fan shaped laser beam; and aposition determining unit to obtain a first set of detection signalsfrom the detector elements, determine at least one first time relationbetween the detection signals of the first set, and determine apositional relation between the detector and the propagation axis basedon the first time relation.
 2. The positioning device according to claim1, wherein the first set of detection signals is obtained from detectorelements arranged along a first line, and wherein the positiondetermining unit is adapted to obtain a second set of detection signalsfrom detector elements arranged along a second line, the first andsecond lines not being parallel with respect to one another; anddetermine at least one second time relation between the detectionsignals of the second set.
 3. The positioning device according to claim1, wherein the first time relation is a first time sequence of thedetection signals of the first set and wherein the position determiningunit is adapted to determine one of at least two segments of a planeintersecting the propagation axis, in which the detector is located. 4.The positioning device according to claim 3, wherein the second timerelation is a second time sequence of the detection signals of thesecond set and wherein the position determining unit is adapted todetermine one of at least four segments of the plane intersecting thepropagation axis, in which the detector is located, based on the firsttime sequence and the second time sequence.
 5. The positioning deviceaccording to claim 2, wherein the detector includes at least threedetector elements (A, B, C), a first connecting line between a first oneof the detector elements (A) and a second one of the detector elements(C) having a first predetermined length (a) not being parallel to asecond connecting line between a third one of the detector elements (C)and the second detector element (B) having a second predetermined length(b); and wherein the first set of detection signals is obtained from thefirst and the second detector elements (A, B) and wherein the second setof detection signals is obtained from the second and the third detectionelements (B, C).
 6. The positioning device according to claim 2, whereinthe position determining unit is adapted to obtain the first set ofdetection signals with the detector having a first orientation and toobtain the second set of detection signals with the detector having asecond orientation rotated with respect to the first orientation.
 7. Thepositioning device according to claim 2, wherein the positiondetermining unit is adapted to determine a repetition time intervalbetween two detection signals from the same detector element and todetermine an angular velocity (ω) of the fan shaped laser beam basedthereon.
 8. The positioning device according to claim 7, wherein theposition determining unit is adapted to determine a first time intervalbetween the detection signals of the first set and a second timeinterval between the detection signals of the second set; determine,based on the angular velocity of the fan shaped laser beam and the firstand second time intervals of a plurality of detector elements, twoangles between the detector elements; and determine, based on the twodetector element angles and the spatial relation of the detectorelements, a distance of the detector to the propagation axis.
 9. Thepositioning device according to claim 8, wherein the positiondetermining unit is adapted to obtain a third and fourth set ofdetection signals with the propagation axis of the fan shaped laser beamof a laser emitter tilted by an angle with respect to the orientation ofthe propagation axis for obtaining the first set and second set ofdetection signals; determine a third time interval between the detectionsignals of the third set and a fourth time interval between thedetection signals of the fourth set; determine, based on the angularvelocity of the fan shaped laser beam and the third and fourth timeintervals of a plurality of detector elements, two other angles betweenthe detector elements; determine, based on the two other detectorelement angles and the spatial relation of the detector elements, asecond distance of the detector to the tilted propagation axis; anddetermine, based on the distance and the second distance, a position ofthe detector with respect to the laser emitter.
 10. The positioningdevice according to claim 8, wherein the position determining unit isadapted to determine a reference angle of one of the detector elementswith respect to a reference orientation and determine a position of thedetector relative to the propagation axis and the reference orientationbased on the reference angle and the distance of the detector to thepropagation axis.
 11. The positioning device according to claim 1,wherein the detector includes at least one level sensor for indicatingat least one reference orientation of the detector in space.
 12. Thepositioning device according to claim 1, further comprising a laseremitter for emitting the fan shaped laser beam rotating around thepropagation axis with the direction of rotation.
 13. A positioningmethod, comprising: detecting light of a fan shaped laser beam rotatingaround a propagation axis with a direction of rotation by a detectorwith at least two detector elements (A, B) arranged in a known spatialrelation to one another and outputting a detection signal whenirradiated by the fan shaped laser beam; obtaining a first set ofdetection signals from the detector elements; determining at least onefirst time relation between the detection signals of the first set; anddetermining a positional relation between the detector and thepropagation axis based on the first time relation.
 14. The positioningmethod according to claim 13, further comprising obtaining the first setof detection signals from detector elements arranged along a first line,and obtaining a second set of detection signals from detector elementsarranged along a second line, the first and second lines not beingparallel with respect to one another; and determining at least onesecond time relation between the detection signals of the second set.15. The positioning method according to claim 13, wherein the first timerelation is a first time sequence of the detection signals of the firstset, and the method further comprising determining one of at least twosegments of a plane intersecting the propagation axis, in which thedetector is located.
 16. The positioning method according to claim 15,wherein the second time relation is a second time sequence of thedetection signals of the second set, and the method further comprisingdetermining one of at least four segments of the plane intersecting thepropagation axis, in which the detector is located based on the firsttime sequence and the second time sequence.
 17. The positioning methodaccording to claim 14, wherein the detector includes at least threedetector elements (A, B, C), a first connecting line between a first oneof the detector elements (A) and a second one of the detector elements(C) having a first predetermined length (a) not being parallel to asecond connecting line between a third one of the detector elements (C)and the second detector element (B) having a second predetermined length(b); and the method further comprising obtaining the first set ofdetection signals from the first and the second detector elements (A,B), and obtaining the second set of detection signals from the secondand the third detection elements (B, C).
 18. The positioning methodaccording to claim 14, further comprising obtaining the first set ofdetection signals with the detector having a first orientation, andobtaining the second set of detection signals with the detector having asecond orientation rotated with respect to the first orientation. 19.The positioning method according to claim 14, further comprisingdetermining a repetition time interval between two detection signalsfrom the same detector element, and determining an angular velocity (ω)of the fan shaped laser beam based thereon.
 20. The positioning methodaccording to claim 19, further comprising determining a first timeinterval between the detection signals of the first set and a secondtime interval between the detection signals of the second set;determining, based on the angular velocity of the fan shaped laser beamand the first and second time intervals of a plurality of detectorelements, two angles between the detector elements; and determining,based on the two detector element angles and the spatial relation of thedetector elements, a distance of the detector to the propagation axis.21. The positioning method according to claim 20, further comprisingobtaining a third and fourth set of detection signals with thepropagation axis of the fan shaped laser beam of a laser emitter tiltedby an angle with respect to the orientation of the propagation axis forobtaining the first set and second set of detection signals; determininga third time interval between the detection signals of the third set anda fourth time interval between the detection signals of the fourth set;determining, based on the angular velocity of the fan shaped laser beamand the third and fourth time intervals of a plurality of detectorelements, two other angles between the detector elements; determining,based on the two other detector element angles and the spatial relationof the detector elements, a second distance of the detector to thetilted propagation axis; and determining, based on the distance and thesecond distance, a position of the detector with respect to the laseremitter.
 22. The positioning method according to claim 20, furthercomprising determining a reference angle of one of the detector elementswith respect to a reference orientation, and determining a position ofthe detector relative to the propagation axis and the referenceorientation based on the reference angle and the distance of thedetector to the propagation axis.
 23. The positioning method accordingto claim 13, further comprising indicating at least one referenceorientation of the detector in space using at least one level sensor.24. A positioning system, comprising: a laser emitter for emitting a fanshaped laser rotating around a propagation axis with a direction ofrotation; a detector having at least two detector elements (A, B)arranged in a known spatial relation to one another for outputting adetection signal when irradiated by the fan shaped laser beam; aposition determining unit to obtain a first set of detection signalsfrom the detector elements, determine at least one first time relationbetween the detection signals of the first set, and determine apositional relation between the detector and the propagation axis basedon the first time relation.
 25. A light emitting device, comprising alaser emitter for emitting a fan shaped laser beam rotating around apropagation axis with a predetermined direction of rotation.
 26. Thelight emitting device according to claim 25, comprising a rotatablecylindrical lens or a rotatable diffraction structure for fanning thelaser beam.
 27. A program including instructions adapted to cause dataprocessing means to carry out the method of claim
 13. 28. A computerreadable medium, in which a program is embodied, where the program is tomake a computer execute the method of claim
 13. 29. A computer programproduct comprising the computer readable medium according to claim 28.